Relay Networks
In a wireless network, such as cellular and ad hoc network, relay nodes can increase the range and the capacity of the network. Relays provide multiple paths between a source node and a destination node to increases the diversity of the network. This can reduce large scale fading due to shadowing.
For the purpose of this description, a simple relay network includes one source node, one relay node, and one destination node. This relay network can give fundamental insights into the design and performance limits of relay networks in general, as described below. This type of network also has practical applications in the design of cellular networks, where the relay node can extend the range of the base station and improve the capacity. The simple relay network can also serve as a building block of larger relay networks.
A number of different protocols are known for relaying packets. An amplify-and-forward (AF) protocol can achieve gains with a simple power boosting circuit at the relay. In a decode-and-forward (DF) protocol, the relay decodes the packet to eliminate noise effects and then re-encodes and retransmits the packet. A compress-and-forward (CF) compresses the data before forwarding. It is known that such relaying protocols can increase achievable data rates.
Split-and-Combine Relaying (SCR) Protocol
In a split-and-combine relaying (SCR) protocol, a packet is split into two fragments and transmitted to the destination in two phases, where the fragments are combined. One method uses a memoryless multiple access channel with cribbing encoders. That method does not consider energy consumption at all. Another method does consider energy consumption. However, the durations of the first and second phases of SCR are fixed to be equal, and independent of the link qualities. Another method analyzes a tradeoff between transmit power and rate of different cooperative techniques in the context of delay-limited capacity in which partial channel state information is known in a time-varying channel. None of the above methods consider the total energy consumption.
Slepian-Wolf Cooperation
Slepian-Wolf cooperation has been used in prior art relay networks. However, there the simultaneous transmissions by the source and relay are not allowed.
The following references teach the prior art SCR and Slepian-Wolf cooperation as summarized above, Willems et al., “The discrete memoryless multiple-access channel with cribbing encoders,” IEEE Trans. Inform. Theory, vol. 31, pp. 313-327, May 1985, Nabar et al, “Fading relay channels: performance limits and space-time signal design,” IEEE J. Select. Areas Commun., vol. 22, pp. 1099-1108, August 2004, Yang et al., “Resource allocation for cooperative relaying,” in 42nd Annual Conf. on Inform. Sci. and Sys., pp. 848-853, March 2008, Gunduz et al., “Opportunistic cooperation by dynamic resource allocation,” IEEE Trans. Wireless Commun., vol. 6, pp. 1446-1454, April 2007, Li et al. “Slepian-Wolf cooperation: a practical and efficient compress-and-forward relay scheme,” Proc. 43rd Annual Allerton Conf. on Commun., Contr. and Computing, September 2005, Slepian et al., “Noiseless coding of correlated information sources,” IEEE Trans. Inform. Theory, vol. 19, pp. 471-480, July 1973, and Van der Meulen et al, “A survey of multi-way channels in information theory: 1961-1976,” IEEE Trans. Inform. Theory, vol. 23, pp. 1-37, January 1977, all incorporated herein by reference.
None of the conventional protocols consider how transmission powers and transmission data rates affect the overall energy consumption in the network. If the effect were known, then energy consumption could be optimized.